In the last year, 34 researchers have used the resources of the Laboratory of Cellular and Molecular Biology Microscopy Core. While most of the researchers come from the Laboratory of Cellular and Molecular Biology, the Core has been used by scientists from the Laboratory of Metabolism, the Mammary Biology and Tumorigenesis Laboratory (Stem Cell Biology Section), the Cell and Cancer Biology Branch, the Laboratory of Experimental Carcinogenesis and the Experimental Immunology Branch (Human Immunology Section). Almost all of the Principal Investigators in the Laboratory of Cellular and Molecular Biology have projects that involve the Core facility. Dr. Lawrence Samelson uses Core resources for the project "Biochemical Basis of T Cell Activation". Researchers working with Dr. Carol Clayberger have used the facility for the projects "Regulation of RANTES Expression in T Lymphocytes" and "Function of Granulysin". The Core has been involved with two projects from Dr. Stanley Lipkowitz, "Identification of Molecular Targets in Triple Negative Breast Cancer" and "Cbl Proteins as Regulators of Tyrosine Kinase Signaling". Dr. Carole Parent's project, "Signaling Events Regulating Chemotaxis" uses all of the Core instruments. Dr. Paul Randazzo has made extensive use of the Core for the project "Regulation of ADP-ribosylation factor". The Core facility has assisted Dr.Jeffry Rubin with the project "Secreted Frizzled-Related Proteins and Wnt Signaling". Dr. Ying Zhang uses Core instruments for the project "Molecular Mechanisms of TGF-beta Signaling Pathway". In addition, the Core facility has been used by personnel working with Principal Investigators from other groups including work with Dr. Michael Bustin on the nucleosome binding protein HMGN1 and the role of heterochromatin formation in cell migration, a project of Dr. Gilbert Smith on channeling mouse ES cells into mammary epithelial precursors, a project of Dr. Zhenggang Liu on cellular localization of the ATIA protein and its mutants and a project of Dr.Kathleen Kelly to characterize normal and transformed prostate epithelial cells in 2-D and 3-D cultures. In work done with Dr. Lawrence Samelson, the Core PI has been the lead investigator in the project, "The Cell Biology of the Calcium Release-Activated Calcium Channel in T Cells". While this project is presented in his annual report, a brief summary is also included here. We obtained fluorescently tagged versions of the calcium detector, STIM1, and the calcium channel subunit, Orai1, and expressed them in T cells. We detected the clustering and colocalization of these two molecules in punctae near the contact surface upon T cell antigen receptor activation. We also observed the colocalization of these molecules at the opposite pole of the activated T cells in cap-like structures. The formation of the caps depended on T cell antigen receptor activation, did not involve restructuring of the entire endoplasmic reticulum and was affected by disruption of the cytoskeleton. The caps were also very dynamic and their content was observed to migrate to the sites of interaction of the T cells with antigen presenting cells. The function of these caps is under investigation.